linux-ext4 - Re: [PATCH 3/7] ext2: Avoid DAX zeroing to corrupt data

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Date:	Mon, 16 May 2016 17:22:06 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Jan Kara <jack@...e.cz>, linux-nvdimm@...ts.01.org,
	Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 3/7] ext2: Avoid DAX zeroing to corrupt data

On Thu 12-05-16 12:45:22, Ross Zwisler wrote:
> On Wed, May 11, 2016 at 11:58:49AM +0200, Jan Kara wrote:
> > Currently ext2 zeroes any data blocks allocated for DAX inode however it
> > still returns them as BH_New. Thus DAX code zeroes them again in
> > dax_insert_mapping() which can possibly overwrite the data that has been
> > already stored to those blocks by a racing dax_io(). Avoid marking
> > pre-zeroed buffers as new.
> > 
> > Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > Signed-off-by: Jan Kara <jack@...e.cz>
> > ---
> >  fs/ext2/inode.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> > index 6bd58e6ff038..1f07b758b968 100644
> > --- a/fs/ext2/inode.c
> > +++ b/fs/ext2/inode.c
> > @@ -745,11 +745,11 @@ static int ext2_get_blocks(struct inode *inode,
> >  			mutex_unlock(&ei->truncate_mutex);
> >  			goto cleanup;
> >  		}
> > -	}
> > +	} else
> > +		set_buffer_new(bh_result);
> >  
> >  	ext2_splice_branch(inode, iblock, partial, indirect_blks, count);
> >  	mutex_unlock(&ei->truncate_mutex);
> > -	set_buffer_new(bh_result);
> >  got_it:
> >  	map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
> >  	if (count > blocks_to_boundary)
> > -- 
> > 2.6.6
> 
> Interestingly this change is causing a bunch of xfstests regressions for me
> with ext2 + DAX.  All of these tests pass without this one change.

Good catch. Attached patch fixes this issue for me. Preferably it should be
merged before the above ext2 change.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

View attachment "0001-ext2-Fix-block-zeroing-in-ext2_get_blocks-for-DAX.patch" of type "text/x-patch" (1210 bytes)